codeforces 620D Professor GukiZ and Two Arrays

 #include <bits/stdc++.h>

 using namespace std;

 const int maxn =  + ;

 const long long inf = 1e18;

 int n, m;

 long long suma, sumb;

 int a[maxn], b[maxn];

 long long dbl_a[maxn], dbl_b[maxn];

 long long sum_dbl_a[maxn * maxn + ], sum_dbl_b[maxn * maxn + ];

 int main()
 {
     map<int, int> pos_a;
     scanf("%d", &n);
     for(int i = ; i <= n; ++i){
         scanf("%d", &a[i]);
         suma += a[i];
         dbl_a[i] = a[i] * ;
         pos_a[dbl_a[i]] = i;
     }

     map<long long, pair<int, int>> m_a;
     map<int, long long> two_pos_a;
     int cnt_a = , cnt_b = ;
     for(int i = ; i <= n; ++i){
         for(int j = i + ; j <= n; ++j){
                 m_a[dbl_a[i] + dbl_a[j]] = make_pair(i, j);
                 sum_dbl_a[++cnt_a] = dbl_a[i] + dbl_a[j];
         }
     }
     scanf("%d", &m);
     for(int i = ; i <= m; ++i){
         scanf("%d", &b[i]);
         sumb += b[i];
         dbl_b[i] = b[i] * ;
     }

     long long diff = (suma - sumb);

     if(diff == ) {
         printf("0\n0\n");
         return ;
     }

     sort(dbl_a+, dbl_a++n);

     long long one_swap_ans = abs(suma - sumb);
     long long two_swap_ans = abs(suma - sumb);
     int one_swap_a = , one_swap_b = ;
     int two_swap_a_1 = , two_swap_a_2 = , two_swap_b_1 = , two_swap_b_2 = ;

     for(int i = ; i <= m; ++i){
         long long tmp = diff + dbl_b[i];
         int pos = lower_bound(dbl_a+, dbl_a+n+, tmp) - dbl_a;
         //printf("%d\n", pos);
         long long big_res = inf;
         if(pos <= n) big_res = dbl_a[pos-];

         long long small_res = inf;
         if(pos -  >= ) small_res = dbl_a[pos - ];

         if(abs(big_res - tmp) > abs(small_res - tmp)){
                 //printf("%d %d %d\n",pos_a[10], dbl_a[pos-1], pos);
                 long long temp = abs(small_res - tmp);
                 if(one_swap_ans > temp){
                         one_swap_ans = temp;
                         one_swap_a = pos_a[dbl_a[pos-]], one_swap_b = i;
                 }
         } else {
                 long long temp = abs(big_res - tmp);
                 if(one_swap_ans > temp){
                         one_swap_ans = temp;
                         one_swap_a = pos_a[dbl_a[pos]], one_swap_b = i;
                 }
         }

     }

     sort(sum_dbl_a + , sum_dbl_a + cnt_a + );

     for(int i = ; i <= m; ++i){
         for(int j = i + ; j <= m; ++j){
                 long long tmp = diff + dbl_b[i] + dbl_b[j];
                 int pos = lower_bound(sum_dbl_a+, sum_dbl_a+cnt_a+, tmp) - sum_dbl_a;
                 long long big_res = inf;
                 if(pos <= cnt_a) big_res = sum_dbl_a[pos];

                 long long small_res = inf;
                 if(pos -  >= ) small_res = sum_dbl_a[pos - ];

                 if(abs(big_res - tmp) > abs(small_res - tmp)){
                         long long temp = abs(small_res - tmp);

                         if(two_swap_ans > temp){
                                 two_swap_ans = temp;
                                 two_swap_a_1 = m_a[sum_dbl_a[pos-]].first;
                                 two_swap_a_2 = m_a[sum_dbl_a[pos-]].second;
                                 two_swap_b_1 = i;
                                 two_swap_b_2 = j;
                         }
                 } else {
                         long long temp = abs(big_res - tmp);

                         if(two_swap_ans > temp){
                                 two_swap_ans = temp;
                                 two_swap_a_1 = m_a[sum_dbl_a[pos]].first;
                                 two_swap_a_2 = m_a[sum_dbl_a[pos]].second;

                                 two_swap_b_1 = i;
                                 two_swap_b_2 = j;
                         }
                 }

                 }
     }

         long long ans = min(abs(diff), min(abs(one_swap_ans), abs(two_swap_ans)));
         printf("%I64d\n", ans);
         if(ans == diff){
                 printf("0\n");
         } else if(one_swap_ans == ans){
                 printf("1\n");
                 printf("%d %d\n", one_swap_a, one_swap_b);
         } else {
                 printf("2\n");
                 printf("%d %d\n", two_swap_a_1, two_swap_b_1);
                 printf("%d %d\n", two_swap_a_2, two_swap_b_2);
         }

     return ;
 }

只交换一次的情况
原来 |Suma - Sumb|
交换后 Suma - xi + yj - (sumb - yj + xi) = suma - sumb + 2(yj - xi) -> 0
则在确定xi的情况下 需要在 b序列里找到 最接近 xi 的 (suma - sumb) /2 + yj的 yj

交换两次的情况
原来 |suma - sumb|
交换后 Suma - xi - xj + yk + yl - (sumb + xi + xj - yk - yl) = suma - sumb + 2((yk + yl) - (xi + xj)) -> 0
则在确定 xi xj的情况下 需要在b序列里找到 最接近 xi + xj的 (suma - sumb)/2 + yk + yl的 yk 和 yl